Figure 6.3 STORAGE BASIN AREA OF INFLUENCE INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO. sm0914f ai

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1 sm0914f ai Figure 6.3 STORAGE BASIN AREA OF INFLUENCE INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO

2 6.6 PRELIMINARY MODELING RESULTS FOR THE STORAGE ALTERNATIVES Following the preliminary screening exercise, Arcadis modeled the three remaining sites assuming the existing conveyance system with planned CIP projects configuration, and using the projected 2035 population data. Model simulations were run to determine the storage required at each location in order to reduce or eliminate SSOs downstream in the collection system. Four separate model scenarios were developed including: 1. Full Conveyance - Model full conveyance of sewage to the WWTP. 2. Add sufficient storage at the Bay Meadows Phase 2 Park to reduce the total flow to the WWTP to 80 mgd, eliminate SSOs in the upstream conveyance pipelines, and reduce surcharge downstream. 3. Add storage at San Mateo High School, and determine the size of required storage to eliminate SSOs upstream and reduce surcharge downstream. 4. Add storage at Abbott Middle School, and determine the size of required storage to eliminate SSOs upstream and reduce surcharge downstream. Under all scenarios, the model included all planned CIP projects and the Dale Avenue PS was sized as necessary to convey flows. In addition, minor cross-connections were made to improve collection system function. As required, pipeline diameters were then modified to eliminate SSOs and to reduce surcharge in the conveyance pipes to greater than 3 feet below grade under a 5-year, 6-hour design storm. If a planned CIP pipeline project could be downsized or eliminated and still meet these criteria, it was noted. Table 6.4 summarizes the flows to the Dale Avenue PS and storage basin for each of the scenarios evaluated as part of the February 2014 modeling simulations. This table also summarizes the storage equalization basin sizing and any modifications to the planned CIP projects for each scenario. The model results demonstrated that in-system storage at Abbott Middle School and San Mateo High School did not provide any significant benefits in terms of SSO elimination, trunk sewer surcharge reduction, or lower capital improvement costs. These two alternatives were eliminated from further analysis. 6.7 FINAL MODELING OF STORAGE ALTERNATIVES Based upon the preliminary modeling results, the City, Arcadis, and Carollo Engineers identified four wastewater/conveyance system/in-system storage system alternatives to be modeled to determine the preferred overall storage approach: 1. Alternative 1 Full Conveyance with storage at the WWTP. Onsite storage sized to limit PWWF through the secondary treatment train to 60 mgd. 2. Alternative 2 - Bay Meadows Storage sized to eliminate the South Trunk Sewer Project. October 2014 FINAL DRAFT 6-14 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

3 3. Alternative 3 - Bay Meadows Storage sized to limit flow to the Dale Avenue PS to the firm capacity of 67 mgd. 4. Alternative 4 - Bay Meadows Storage sized with the smallest sizing necessary to eliminate downstream SSOs and reduce surcharge to acceptable levels. Table 6.4 Storage Location Detroit Drive Parcel (WWTP) Bay Meadows Phase 2 Park Preliminary Model Results for Storage Basins Integrated Wastewater Master Plan City of San Mateo Peak Wet Weather Flow to Storage (mgd) 98.0 total to WWTP Peak Wet Weather Flow to Dale Ave PS (mgd) Recommended Storage Size (MG) Abbott Middle School San Mateo High School Modifications to Planned CIP Improvements? New 17.1 mgd Dale Ave. wet weather pump station required. Reduces 7,000 feet of South Trunk Phase 2 pipe from 42 /48 to 24 diameter. Eliminates SST 5 Hacienda Flores Relief Project. Provided minimal PWWF reduction The following sections discuss the results of these analyses Alternative 1: Full Conveyance Alternative with Storage at the WWTP (7.7 MG) Alternative 1 entails full conveyance of all flows to the WWTP with wet weather storage adjacent to the WWTP at the Detroit Drive property. Due to space limitations at the WWTP, the Detroit Drive location was identified as the most cost effective location for a large, below grade basin. Under this alternative, model simulations assumed that all planned capital improvements were implemented and flows to the WWTP were not limited by the current capacity of the Dale Avenue PS. This alternative results in a flow of 84.1 mgd to the WWTP from Dale Avenue PS, and will require a new upsized Dale Avenue PS (17.1 mgd capacity). The inclusion of flows from the Shoreview/Los Prados area (2.7 mgd), Mariner s Island (1.6 mgd), and EMID (9.5 mgd) make a total flow of 98.0 mgd to the WWTP influent junction box. The storage basin adjacent to the WWTP was sized using the Year 2035 flow hydrograph produced by the model (see Appendix K) and limiting flows to the secondary treatment system to 60 mgd, which resulted in a 7.7 MG buried storage tank. With this alternative, two major changes to the collection system planned CIP projects were identified and are summarized in Table 6.5. October 2014 FINAL DRAFT 6-15 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

4 One advantage to locating the storage facility adjacent to the WWTP, is that it provides the WWTP with some flexibility in operations, especially during the construction of large projects. The major disadvantage of this location is that immediate relief within the collection system is not provided, as would be with an in-system storage basin. In addition, conveyance facilities will need to be sized to convey PWWF to the WWTP. Table 6.5 Alternative 1 Major Changes to Planned Collection System Projects Integrated Wastewater Master Plan City of San Mateo Project ID Project Title Major Additions or Changes to CIP Projects WW-03 DAX-3 New Flow Equalization Storage New Dale Avenue Wet Weather PS Build new 7.7 MG storage basin at the corporation yard. Build new 17.1 mgd Dale Avenue Wet Weather PS Alternative 2: In-System Storage at Bay Meadows Park (12.8 MG) Alternative 2 looked at providing sufficient storage at the Bay Meadows Park to eliminate Phase 2 of the South Trunk Sewer Project (7,000 feet of 42-inch and 48-inch pipe). Under this alternative, model simulations assumed that all planned capital improvements were implemented and flows to the WWTP were not limited by the current capacity of the Dale Avenue PS. This alternative requires the construction of a 12.8 MG equalization basin. A basin this size would also reduce surcharge and eliminate SSOs in the area. This alternative does not eliminate storage at the WWTP, but reduces the volume required from 7.7 MG to 2.6 MG. Flow to Dale Avenue PS is reduced to 58.7 mgd (which is within its current capacity), so that a new wet weather pump station project would not be required under this alternative. Table 6.6 summarizes the major changes to the collection system planned CIP projects under this alternative. Table 6.6 Alternative 2 Major Changes to Planned Collection System Projects Integrated Wastewater Master Plan City of San Mateo Project ID Project Title Major Additions or Changes to CIP Projects WW-03 New Flow Equalization Storage Build new 2.6 MG storage basin at the corporation yard SAT-2 South Trunk Sewer Phase II Eliminate project of 7,000 feet of 42 /48 pipe SAT-3 South Trunk Phase III Build new 12.8 MG storage basin at the Bay Meadows Park The Bay Meadows Park was recently built as part of the Bay Meadows Phase II development, and current improvements include baseball fields and open grass areas. With a usable storage depth of 8 feet, a basin approximately 570 feet long by 350 feet wide would be required. Under this alternative, the entire park would require reconstruction, October 2014 FINAL DRAFT 6-16 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

5 which may cause some opposition by the residents. The cost and difficulty of constructing a 12.8 MG below-grade equalization tank outweighs the benefits of not building the South Trunk Sewer Project, and it was agreed that this alternative be eliminated from further consideration Alternative 3: In-System Storage at Bay Meadows Park (4.2 MG) Alternative 3 also provided wet weather storage at Bay Meadows Park sized to reduce surcharge and eliminate SSOs in the area and limit flows to the Dale Avenue PS to less than its maximum capacity of 67 mgd. This scenario resulted in a 4.2 MG equalization basin at Bay Meadows Park, while eliminating the need to upgrade the Dale Avenue PS. In addition, the conveyance pipelines in the Phase 2 of the South Trunk Sewer Project was downsized to 36 inches (from 42 inch and 48 inch pipe), and was still able to limit surcharge of the collection system to greater than 3 feet below grade. This alternative also requires construction of 4.0 MG of storage at the WWTP. The advantage of having two storage tanks (in-system and at the WWTP) is that it provides WWTP operators with much more flexibility for shut down of certain process trains during the major upcoming improvements. With a usable depth of 8 feet for storage, a basin approximately 350 feet long by 200 feet wide would be required. This alternative would entail reconstruction of the grass fields portion of the park. Table 6.7 summarizes the major changes to the collection system planned CIP projects under this alternative. Table 6.7 Alternative 3 Major Changes to Planned Collection System Projects Integrated Wastewater Master Plan City of San Mateo Project ID Project Title Major Additions or Changes to CIP Projects WW-03 New Flow Equalization Storage Build new 4.0 MG storage basin at the Detroit Drive Parcel SAT-2 South Trunk Sewer Phase II Reduce size of 7,000 feet of 42 /48 pipe to 36 pipe SAT-3 South Trunk Phase III Build new 4.2 MG storage basin at the Bay Meadows Park Alternative 4: In-System Storage at Bay Meadows Park (3.2 MG) Alternative 4 provides for the minimum wet weather storage at Bay Meadows Park, which was sized to reduce surcharge to acceptable levels and to eliminate SSOs in the area. This resulted in a 3.2 MG equalization basin in the collection system and a 5.6 MG storage basin at the WWTP. With a usable depth of 8 feet for storage, a basin approximately 350 feet by 150 feet would be required at the park, and would need reconstruction of the grass fields portion of the park. A new Dale Avenue PS wet weather pump station with 6.6 mgd capacity would be required under this alternative. Table 6.8 summarizes the major changes to the collection system planned CIP projects under this alternative. October 2014 FINAL DRAFT 6-17 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

6 Table 6.8 Alternative 4 Major Changes to Planned Collection System Projects Integrated Wastewater Master Plan City of San Mateo Project ID Project Title Major Additions or Changes to CIP Projects WW-03 DAX-3 New Flow Equalization Storage New Dale Avenue Wet Weather Pump Station Build new 5.6 MG storage basin at the Detroit Drive Parcel Build new 6.6 mgd Dale Avenue Wet Weather PS SAT-2 South Trunk Sewer Phase II Reduce size of 3,900 feet of 48 pipe to 42 pipe SAT-3 South Trunk Phase III Build new 3.2 MG storage basin at the Bay Meadows Park CIP Modifications Common to All Alternatives Each of the alternatives evaluated resulted in some modifications to the planned CIP. Common modifications to the four alternatives are summarized below in Table 6.9. Table 6.9 Changes to Planned CIP Projects Common to All Alternatives Integrated Wastewater Master Plan City of San Mateo Project ID Project Title Major Additions or Modifications to CIP Projects SST-3 South Delaware/Bay Meadows Parallel Line SAT-1 South Trunk Phase 1 LPS-5 LPS-6 LPS-7 SNT-X5 SST-X2 SST-X3 SST-X5 Kehoe-Van Buren Relief Sewer Los Prados Replacement Los Prados 3 to Bahia Edinburgh St/Sonora Dr Relief El Camino Relief Extension 38th to 36th Hillsdale Relief Extension ADLP to Hacienda Yew St Relief Barneson to Hwy 92 Upsize diameter of 3,250 feet of 21 pipe to be installed to 36. Upsize 70 feet of 48 pipe to 60 downstream of Phase 1 and influent to DAPS wet well Upsize diameter of 1,500 feet of 12 pipe to be installed to 15 and 2,950 feet of 15 pipe to 18 New project: Upsize 2,100 feet of existing 21 sewer to 24 from Hancock to Highway 101 New project: Upsize 1,040 feet of existing 8 sewer to 10 from Los Prados 3 to Bahia Add to project: Upsize 120 feet of existing 8 sewer to 12 from MH X to MH303-07X. Add to project: Upsize 900 feet of existing 15 sewer to 18 from 36th to Hillsdale; upsize 40 feet of pipe from 15 to 24 at Hillsdale/El Camino, and upsize 450 feet of 24 to 30 from Hillsdale to 450 feet south of 31st. Add to project: Upsize 350 feet of existing 8 sewer to 12 from MH X to MH X Add to project: Upsize 79 feet of existing 10 sewer to 12 from MH X to MH X and upsize 200 feet of 8 sewer to 10 from MH X to MH X. October 2014 FINAL DRAFT 6-18 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

7 6.8 ALTERNATIVES COMPARISON The evaluation of the proposed storage alternatives took into consideration both economic and non-economic criteria. A set of evaluation criteria, consistent with the goals and objectives of the City, were developed to compare the alternatives. As the City has adopted sustainability goals and objectives, it was recommended that the Triple Bottom Line framework be used to evaluate the benefits and impacts of an alternative in the following areas: financial (costs), social (community), and environmental (reduction of SSOs). In addition, the criteria included a wastewater system operations category to consider technical criteria in evaluating storage size and location. Table 6.10 summarizes the criteria used in this analysis. Table 6.10 Alternatives Evaluation Criteria Integrated Wastewater Master Plan City of San Mateo Wastewater System Operations Costs Community Environment Flexibility of Operations Capital Costs Noise Reduction of SSOs Cleaning Effort Odor Ease of Access Visual Constructability For the purposes of comparing the alternatives, the evaluation criteria were split into economic and non-economic evaluations. The criteria for the wastewater system operations, community, and environment criteria are considered in the non-economic evaluation section of this chapter, while the criteria for the costs are considered in the economic evaluation section Non-Economic Evaluation For the non-economic evaluation of alternatives, a qualitative approach was used for all criteria. A comparison of the alternatives for the wastewater system operations, community, and environment categories is shown in Table For the wastewater system operations criteria, the alternatives differ significantly in the flexibility provided to the WWTP operations. The following is a summary of the non-economic evaluation of the proposed alternatives: Storage at the Detroit Drive site provides convenient local storage that can be used in the dry season by the WWTP to take other processes off line for repair or during construction, as needed. This site would be the most easily accepted by the community, since the WWTP is already located in the vicinity and there would be minimal change to noise, odor, or visual impacts. However, this alternative does not score well on environment, since it would not provide any relief to surcharge in the collection system. October 2014 FINAL DRAFT 6-19 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

8 Table 6.11 Alternative 1 Alternative 2 Alternative 3 Alternative 4 Legend: Summary of the Qualitative Screening Evaluation Integrated Wastewater Master Plan City of San Mateo Wastewater Alternative Description System Operations Community Environment Full Conveyance 12.8 MG Basin at Bay Meadows Park 4.2 MG Basin at Bay Meadows Park 3.2 MG Basin at Bay Meadows Park Meets criteria Partially meets criteria Does not meet criteria Alternative 2, the 12.8 MG storage at Bay Meadows, provides the most wet weather relief in the area of the collection system most prone to surcharge and SSOs, and ranks highly in this category. However, the large footprint and difficulty in construction led to a lower community score. In addition, while eliminating the South Trunk Sewer Project would help offset the costs of the large basin, it reduces flexibility in wastewater system operations by significantly reducing storage at the WWTP that is useful during repairs or rehabilitation at the WWTP. Alternative 3 provides the most operational flexibility since flow could either be reduced coming into the WWTP or an equivalent amount could be stored at the WWTP, with approximately 4.2 MG of storage provided at each location. Alternative 4 with 3.2 MG of storage does an adequate job of reducing SSOs, aiding system operations, and has less of an impact to the community than the larger basins. However, this alternative did not score high for any of the criteria. Each of the Bay Meadows alternatives allows the operators to reduce flow coming into the WWTP by varying amounts, but does not allow the flow to be diverted during construction since the storage basin location is 4.5 miles away from the WWTP. A large basin in the collection system does not eliminate the need for storage at the WWTP to meet peak flows to the WWTP. While two storage basins will require more operations and maintenance time and money, they also provide more flexibility. In addition, each of the in-system storage basin alternatives provides the potential for recycled water storage benefits. As the City s recycled water planning is in its infancy, conceptual plans did not look at storage to meet peak irrigation demands. Since the irrigation season is during the dry season, there may be an opportunity to use the wet weather basin storage for the recycled water system without additional cost. October 2014 FINAL DRAFT 6-20 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

9 Based on non-economic factors, Alternatives 1 and 3 received the highest and approximately equivalent scores. Figure 6.4 shows the space required to accommodate 7.7 MG of storage on the Detroit Drive site (Alternative 1). Figure 6.5 is an aerial of the Bay Meadows site (Alternative 3) and shows an approximate sizing for the proposed 4.2 MG storage. The exact location available for storage on the Bay Meadows site is still undetermined, as the property will be a shared site with Parks and Recreation Economic Evaluation Construction and total project costs were prepared for each of the storage alternatives. The capital costs are presented in August 2014 dollars, which corresponds to a San Francisco Engineering News Record Construction Cost Index (ENR CCI) of Costs were prepared in accordance with the guidelines of the Association for the Advancement of Cost Engineering International (AACE International), 18R-97 for a Class 5 estimate. Appendix D provides the Basis of Cost used for all projects in the Integrated Wastewater Master Plan. Annual operation and maintenance (O&M) costs are assumed to be negligible compared to the capital cost and roughly equivalent for all alternatives since a small pump station, that would only be operated occasionally after wet weather events, would be required for each alternative. The only difference between the WWTP storage and the three Bay Meadows storage facilities is that off-site maintenance and cleaning would be required for the Bay Meadows alternatives resulting in a minimal increase in cost for the Bay Meadows sites associated with travel time and set-up. Table 6.12 summarizes the construction and total project costs, while details are provided in Appendix L Assumptions This section contains a list of general and site specific assumptions made during the cost estimating effort for all four alternatives: Reinforced concrete equalization basin. Top of basin would be 5 feet below grade, except at the Detroit Drive site where the basin cover would be at grade level. Two feet of freeboard would be used to prevent pressurization of basin. Basin would be divided into three compartments to allow sequential filling of compartments to minimize cleaning after each use. Excavated materials would not be suitable without pre-treatment for backfill. Imported materials would be used. (Final Geotechnical Investigation for Infrastructure Improvements, Bay Meadows Phase 2 dated September 2008 by Treadwell & Rollo). November 2014 FINAL DRAFT 6-21 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

10 LEGEND Corporation Yard WWTP Site Storage Basin Buried Tank 250 x 400 Figure MG STORAGE AT DETROIT DRIVE SITE INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO sm0914f ai

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12 Approximate size of 4.2 MG storage (350 x 200 ). Exact location is not determined and will be coordinated with the Parks Department. e h Av E 25 th Av e E t 25 S De la w ar e St Figure MG STORAGE TANK AT BAY MEADOWS PARK INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO sm1114f ai

13 Equalization basin would be fed via a below grade pump station structure located in the street. Cost of all influent piping/overflow structure have been included in the cost. Odor control system would consist of above-grade air scrubber system adjacent to equalization basin. Underground access would only be required for cleaning and access to pump station. A new below grade raw sewage pump station with three submersible pumps and comminutors (grinders) that pumps to 10 feet below grade would be used. No bar screens would be provided. Flow from the basin back to the collection system would be via gravity. Pipe size is based on emptying the entire basin within a 48-hour period after a wet weather event. Effluent piping would run from the equalization basin to closest sewer trunk line in adjacent street. Allowable soil bearing capacity is 2000 pounds per square foot (psf). (Based on Geotechnical Exploration for the South Trunk Sanitary Sewer Relief Line dated April 2011 by ENGEO Inc.). Soils with hydrocarbon contamination would be hauled to Ox Mountain Landfill in Half-Moon Bay. (Landfill determined by closest landfill to project that accepts soils with petroleum on the San Francisco Bay RWQCB Region 2 Landfill Waste Acceptance List). Groundwater with hydrocarbon contamination would be treated on site. (None of the landfills listed on the San Francisco Bay RWQCB Region 2 Landfill Waste Acceptance List accepted designated liquids). October 2014 FINAL DRAFT 6-24 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

14 Table 6.12 In-System Equalization Basin Cost Integrated Wastewater Master Plan City of San Mateo Storage Alternative Construction Cost (1) ($M) Total Project Cost (1) ($M) Alt 1 Full Conveyance N/A N/A Alt MG Storage at Bay Meadows Park Alt MG Storage at Bay Meadows Park Alt MG Storage at Bay Meadows Park $54.5 $77.9 $22.3 $31.9 $18.0 $25.7 Note: (1) Costs are provided as present value based on a ENR CCI number of corresponding to the San Francisco Index in August Costs are not escalated to future years. Total project costs include a 35 percent construction cost estimating contingency and 45 percent allowance for engineering, CEQA, legal, administration, construction management, and 10% unallocated contingency. 6.9 ALTERNATIVES COMPARISON WITHIN THE OVERALL WASTEWATER SYSTEM A comparison of the proposed alternatives is incomplete without evaluating how they fit into the overall wastewater system. An in-system storage basin does not necessarily eliminate the need for storage at the WWTP, since peak flows through the secondary treatment train and outfall must be limited to 60 mgd. In addition, the need for and size of a wet weather pump station at Dale Avenue is determined by the flow to the Dale Avenue PS during wet weather events, which is dependent upon the in-system storage size. The size of primary treatment facilities is dependant upon the flow from the Dale Avenue PS to the WWTP. Table 6.13 provides a more complete comparison of wastewater system costs in relation to storage, rather than focusing only on the cost of a single storage basin. As shown, 4.2 MG of in-system storage achieves the lowest overall cost. However, the overall costs for the four alternatives can be considered to be equivalent as they are all within the range of accuracy of this planning level cost estimate RECOMMENDED ALTERNATIVE Based on the economic and non-economic evaluation, Alternative 3 (4.2 MG in-system storage) is the recommended alternative, as it is the lowest cost alternative and provides the most benefits for operations and SSO reduction. In addition, providing in-system storage greatly reduces the size of the preliminary and primary treatment facilities and flow equalization at the WWTP, which is already a tight site. Alternative 1 (Full Conveyance) is a October 2014 FINAL DRAFT 6-25 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

15 viable alternate that should be carried through California Environmental Quality Act (CEQA) review for final determination of a preferred alternative. October 2014 FINAL DRAFT 6-26 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx

16 October 2014 FINAL DRAFT 6-27 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_06.docx Table 6.13 Design Criteria Wastewater Storage Alternatives Cost Comparison Integrated Wastewater Master Plan City of San Mateo Alternative 1 Full Conveyance Alternative MG EQ Basin Alternative MG EQ Basin Alternative MG EQ Basin PWWF to WWTP (mgd) Total PWWF through New WW Dale Avenue PS (mgd) In-System Storage (MG) Storage at Detroit Drive (MG) Project Costs ($M) In-system Storage w/ Odor Control -- $78.98 $32.35 $26.06 New Dale Avenue PS w/ Odor Control $ $6.21 Headworks w/ Odor Control $49.42 $40.21 $42.21 $45.68 Sedimentation Basins w/ Odor Control $47.71 $38.00 $40.11 $43.78 Detroit Drive Storage w/ Odor Control $52.45 $22.05 $31.13 $40.67 Collection System Pipeline Projects $68.74 $44.05 $63.56 $66.82 Total Project Cost $ $ $ $ Note: (1) Costs are provided as present value based on a ENR CCI number of corresponding to the San Francisco Index in August Costs are not escalated to future years. Total project costs include a 35 percent construction cost estimating contingency and 45 percent allowance for engineering, CEQA, legal, administration, construction management, and 10% unallocated contingency.

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18 Chapter 7 WWTP EXISTING FACILITIES AND CAPACITY EVALUATION 7.1 PURPOSE This chapter provides an overview of the existing facilities at the City of San Mateo (City)/Estero Municipal Improvement District (EMID) jointly owned Wastewater Treatment Plant (WWTP) and includes the following: A description of existing facilities including the general function and configuration of the major liquid and solid stream treatment processes at the WWTP. A history of WWTP projects, including projects implemented to accommodate growth, and projects to address new regulatory requirements. A performance assessment summarizing the historical treatment performance of the overall WWTP and the performance of each major unit process. A capacity assessment summarizing the hydraulic and process capacity of each major unit process and the overall capacity of the WWTP. 7.2 SUMMARY OF KEY FINDINGS Performance Assessment The key findings and recommendations of the performance assessment include the following: During the five-year review period, the WWTP final effluent was in full compliance with all discharge requirements included in the WWTP s National Pollutant Discharge Elimination System (NPDES) permit. The performance of the primary clarifiers, with regards to carbonaceous biochemical oxygen demand (CBOD) and total suspended solids (TSS) removal, could not be evaluated directly for the entire review period because primary effluent samples are not collected and analyzed regularly. However, primary effluent data was collected as part of the wastewater characterization sampling program conducted in May This data was used to evaluate the performance of the primary clarifiers, which appear to be working well. The process performance data for the aeration basins and secondary clarifiers is provided below: Average solids retention time (SRT) of 2.5 days, assuming four aeration basins in service. October 2014 FINAL DRAFT 7-1 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

19 Average mixed liquor suspended solids (MLSS) concentration of 1,000 milligrams per liter (mg/l). Average sludge volume index (SVI) of 176 milliliters per gram (ml/g); 90th percentile SVI of 255 ml/g. The hydraulic and solids loading rates of the gravity thickeners could not be evaluated, because primary sludge data has not historically been collected by the City. The process loading of the dissolved air floatation thickener (DAFT) was evaluated beginning in February 2012 when the City stopped sending a portion of the waste activated sludge (WAS) to the gravity thickener, to be blended with the primary sludge. The current operational mode is to send WAS to the DAFT and primary sludge to one of the gravity thickeners. In the February through May 2012 time period, the average hydraulic and solids loading rates for the DAFT were 0.5 gallons per minute per square foot (gpm/sf) and 6.8 pounds per day per square foot (ppd/sf), respectively. The performance and process loading for the anaerobic digesters could not be evaluated in the current configuration for the entire review period, because the City only began operating in series mode in October The average volatile solids reduction during the time period from October 2010 until the present was 69 percent. It is recommended that the City conduct additional process monitoring including: Regular monitoring of the primary effluent CBOD and TSS to evaluate process performance more accurately. Periodical monitoring of the primary sludge flow and concentration to evaluate process loading in the gravity thickeners in the future Hydraulic Capacity Analysis The key findings and recommendations of the hydraulic capacity analysis include the following: Primary Clarifiers 1 and 2 are a hydraulic capacity bottleneck, with the effluent weirs becoming submerged when plant influent flow reaches 20 million gallons per day (mgd). The primary clarifiers can not easily be retrofitted to fix this hydraulic limitation, so it is recommended that Primary Clarifiers 1 and 2 be replaced. Findings from the condition assessment, provided in Chapter 8, support this recommendation. The new primary treatment facilities would be designed to handle the recommended hydraulic capacity. There is a significant amount of headloss, at high flows, through the submerged gate and orifice in the Aeration Basin Influent Mixing Box at the head of the influent October 2014 FINAL DRAFT 7-2 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

20 channel, which limits the hydraulic capacity of the primary clarifiers and the aeration basins. Due to the geometry of the aeration basin influent channel, it is difficult to achieve an optimal flow split between the five aeration basins. A computational fluid dynamic (CFD) model of the influent channel is recommended to evaluate and provide recommendations to optimize the flow split. It is recommended that the design of new wastewater treatment processes include the ability to proportionately distribute the flow, such as flow splitting structures Process Capacity Analysis The key findings and recommendations of the process capacity analysis include the following: The liquid treatment process capacity is limited by the MLSS concentration and the solids loading rate of the existing secondary clarifiers under dry weather and wet weather conditions. The calculated limiting clarifier inlet MLSS concentration, with all five clarifiers in service, is approximately 1,650 mg/l assuming that the secondary flow rate is limited to 40 mgd through primary effluent bypass or upstream equalization and all aeration tanks and all secondary clarifiers are in service during wet weather. The equivalent ADWF capacity is approximately 16 mgd. With the exception of the centrifuges, the solids handling facilities have an equivalent ADWF capacity greater than the permitted ADWF of 15.7 mgd. The centrifuge hydraulic capacity of 95 gpm limits the centrifuge process capacity to approximately 14.6 mgd ADWF, with one centrifuge in standby. The simulated peak digested sludge production at this condition requires continuous (24 hours per day, 7 days per week) centrifuge operation. However, the 2003 solids dewatering improvements project included provisions for a second duty (third) centrifuge. This would double the reliable centrifuge hydraulic capacity to 190 gpm, eliminating the need for continuous centrifuge operation to handle peak digested sludge production. 7.3 PLANT HISTORY The WWTP was originally constructed in the 1930s and 1940s and has been expanded over time to accommodate growth in the service area and to provide higher levels of treatment. Major projects at the WWTP, over the years, include the following: Primary Clarifiers 1 and 2 were constructed in 1934 and 1948, respectively. These projects also included appurtenant facilities. In 1953, Primary Clarifier 3 was added to address growth in the service area. In 1968, the Administration Building, the Electrical Shop, and Effluent Pump Station No. 1 were added. October 2014 FINAL DRAFT 7-3 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

21 In 1976, a major expansion of the WWTP, including the addition of secondary treatment, was completed. The following facilities were constructed as part of the expansion: Primary Clarifier 4. Aeration Basins 1 through 4. Secondary Clarifiers 1 through 4. Effluent Pressure Filters. Chlorine Contact Basins 1 and 2. Gravity Thickeners 1 and 2. Solids Handling Building. In 1992, the following facilities were added: Influent Junction Box (IJB). Aeration Basin 5. Secondary Clarifier 5. Sodium Hypochlorite Facility. Sodium Bisulfite Facility. DAFT and Thickener Control Building. Anaerobic Digester 1. In 2005, the City completed a major solids handling project, which included the following facilities: Primary sludge and scum screening equipment. Primary sludge grit removal equipment. Anaerobic Digester 2. Digested Sludge Storage Tank. Centrifuge. Cake conveyance and storage hoppers. Figure 7.1 is a site plan of the WWTP, including all existing facilities, as well as it and illustrates how the WWTP has expanded over the decades. 7.4 DESCRIPTION OF EXISTING TREATMENT FACILITIES Treatment processes at the WWTP consist of primary clarification, secondary treatment through aeration basins and secondary clarifiers, partial effluent filtration, disinfection, and solids handling. Final effluent from the WWTP is pumped to the discharge outfall and discharged into the San Francisco Bay. The facilities are described further in the following sections and a WWTP process flow diagram is provided in Figure 7.2. October 2014 FINAL DRAFT 7-4 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

22 Sludge Storage Tank Digester Control Building Anaerobic Digester 1 Approximate Time of Construction Anaerobic Digester Maintenance Building Biofilter Gas Conditioning Facilities Biofilter Primary Clarifier 4 Solids Handling Building Cake Hopper Influent Junction Box Primary Clarifier 1 Biofilter Primary Clarifier 3 Surge Tank MCC Building Abandoned Facilities Primary Sludge Pump Building Effluent Pump Station #2 Abandoned Facilities Aeration Basins 1 Fuel Oil Storage 2 Effluent Pump Station #1 Electrical Shop Generator #5 Hypochlorite Storage Facility Thickener Control Building Administration Building Primary Clarifier 2 Gravity Sludge Thickeners DAFT Main Treatment Structure Secondary Clarifiers 1 Sodium Bisulfite Storage 1 Chlorine Contact Basins Pump Pit 4 Secondary Clarifier 5 Effluent Filters Figure 7.1 EXISTING FACILITIES LAYOUT INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO sm0914f ai

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24 From Collection System From Collection System From Collection System From Collection System Mariner s Island Lift Station No. 59 (EMID) Dale Ave Pump Station (City) Flint Pump Station Influent Junction Box Primary Sludge and Scum Pumps Primary Clarifiers Aeration Basins RAS Pumps Secondary Clarifiers WAS Pumps Filter Feed Pump Station Effluent Pressure Filters Dissolved Air Flotation Thickeners (DAFTs) Chlorine Contact Basins Effluent Pumping Anaerobic Digester 1 Effluent Outfall Anaerobic Digester 2 Discharge to SF Bay Digested Sludge Storage Tank Centrifuges Sludge Screens Grit Pumps Grit Classifiers Sludge Flow Control Chamber Gravity Thickeners Digester Feed Pumps Cake Pump Cake Hopper Scum Screens Disposal LEGEND Liquid Stream Solids Stream Figure 7.2 EXISTING FACILITIES PROCESS FLOW SCHEMATIC INTEGRATED WASTEWATER MASTER PLAN CITY OF SAN MATEO sm0914f ai

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26 The WWTP has a permitted ADWF capacity rating of 15.7 mgd; and the design peak wet weather flow (PWWF) capacity for each unit process is provided in Table 7.1. Design criteria for each unit process are provided in Appendix M. Table 7.1 PWWF Design Capacity (1) Integrated Wastewater Master Plan City of San Mateo Unit Process PWWF Capacity (mgd) Influent Junction Box 60 Primary Clarifiers (2) 60 Aeration Basins 40 Secondary Clarifiers 40 Effluent Filters 40 Chlorine Contact Basins 60 Outfall 60 Note: (1) PWWF criteria from Contract No , Main Plant Expansion, HDR, May (2) Per hydraulic calculations, performed as part of this analysis, the effluent weirs on Primary Clarifiers 1 and 2 are submerged at a flow above 20 mgd Influent Flow Distribution Raw wastewater from the service area enters the WWTP at the influent junction box (IJB) through four force mains: two 30-inch lines from the Dale Avenue Pump Station (PS), one 20-inch line from EMID, and one 14-inch line from Mariner s Island. The combined influent flow passes through a six-foot parshall flume for influent flow measurement. An ultrasonic level transmitter continuously measures the water surface elevation (WSE) at the flume. This level measurement is converted to flow at the metering panel. Plant recycle flows are brought back into the IJB downstream of the flume, where the influent sample is drawn, so that recycle flows are not included in the influent flow measurement or influent concentrations. The combined influent and recycle flows are distributed over four downward opening weir gates to the four primary clarifiers. The length of each weir gate is proportional to the surface area of the corresponding clarifier, to approximate an appropriate flow split Primary Treatment The primary treatment facilities consist of four primary clarifiers, six primary sludge pumps, and three primary scum pumps. The clarifiers are center-feed, peripheral-withdrawal type clarifiers. In the clarifiers, suspended solids gradually settle to the bottom of the tanks as primary sludge. The primary effluent, the liquid portion of the flow, flows by gravity to the October 2014 FINAL DRAFT 7-7 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

27 secondary treatment facilities. Mechanical scrapers collect settled sludge and skimmer arms collect floatable scum in the primary clarifiers. There are four sludge pumps for Primary Clarifiers 1 through 3 located in the Primary Sludge Pump Building to the east of the clarifiers. Each clarifier has a dedicated sludge pump, with the fourth pump serving as standby. Primary Clarifier 4 has two dedicated sludge pumps, with one serving as standby. The primary sludge pumps pump settled solids from the primary clarifiers to the sludge screens in the Solids Handling Building for pretreatment. There is one scum pump to serve Primary Clarifiers 1 and 2, while Primary Clarifiers 3 and 4 have dedicated scum pumps. The primary scum pumps pump scum from the primary clarifiers to the scum concentrator in the Solids Handling Building. Primary effluent is typically piped to the aeration basins for secondary treatment. During extreme wet weather flow, there is the option to bypass the aeration basins and send a portion (up to 20 mgd) of the primary effluent directly to the chlorine contact basins. In December 2012, Primary Clarifier 3 experienced failure of its sludge collection mechanism. Carollo Engineers, Inc. (Carollo) prepared a technical memorandum (TM) documenting the failure and providing repair recommendations. This TM is provided as Appendix N Secondary Treatment The secondary treatment facilities include five aeration basins, seven aeration blowers, five secondary clarifiers, and return activated sludge (RAS) and waste activated sludge (WAS) pumping systems Aeration Basins Primary effluent enters the aeration basins at the activated sludge mixing box and flows through the aeration basin influent channel, where it is split amongst the five aeration basins via two submerged slide gates per basin. The aeration basins provide biological treatment by maintaining a population of microorganisms that break down organic matter present in the primary effluent. The liquid in the aeration basins is referred to as mixed liquor and the microorganisms, commonly referred to as bugs, include bacteria, protozoa and fungi. The microorganisms are naturally present in wastewater and require food and oxygen to survive. The aeration basins are supplied with dissolved oxygen so the microorganisms metabolize soluble organic matter present in the influent, and grow and multiply. The mixed liquor flows from the aeration basins to the secondary clarifiers, where the microorganisms settle out of the mixed liquor as sludge. To maintain a healthy population of microorganisms in the aeration basins, a portion of the settled sludge is returned to the aeration basins, and is referred to October 2014 FINAL DRAFT 7-8 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

28 as RAS. RAS from the secondary clarifiers is piped back to the aeration basin influent channel for distribution to the aeration basins. Air is distributed to the aeration basins with a fine bubble diffused air system. Approximately 14,840 ceramic diffusers are mounted at the bottom of the aeration basins. To meet the oxygen demand throughout the length of the basin, the diffuser density is tapered in each aeration basin Blowers Seven multi-stage, centrifugal-type blowers supply air to the aeration basins. One blower not operable due to a failure, but has not been repaired due to the redundancy in the system. The units are located in the blower room of the Main Treatment Structure. Four of the blowers are designed to deliver a maximum of 4,450 standard cubic feet per minute (scfm) each; the remaining three blowers deliver a maximum of 7,000 scfm each. Only two of the smaller blowers can be operated on emergency power. The airflow rate through the blowers can be adjusted, if desired, by adjusting the motorized inlet throttling valves. Air from the blowers is discharged into a common header for distribution to the aeration basins. Each aeration basin is equipped with two motorized valves and two laterals, for a total of ten valves and ten laterals. The laterals branch off to grids of polyvinyl chloride (PVC) piping, which are secured to the floor of each basin. The diffusers are mounted on these grids. The diffusers in Aeration Basins 1 through 4 are fine bubble ceramic diffusers, while Aeration Basin 5 has membrane diffusers. Each aeration basin is also equipped with two dissolved oxygen probes, which are used to adjust airflow to maintain a dissolved oxygen setpoint Secondary Clarifiers Mixed liquor flows from the aeration basins, over effluent weirs, and into the collection channel. It then flows through a series of isolation slide gates for distribution into the five secondary clarifiers, four square and one circular. Mixed liquor settles to the bottom of the clarifiers and the clarified liquid portion of the effluent flows over effluent weirs and to the effluent filters for further treatment. Each secondary clarifier has a sludge and scum removal system. If the effluent filters are in service, secondary effluent is collected and a portion is piped to the Filter Feed Pump Station. If the effluent filters are not in service, secondary effluent flows by gravity to the influent mixing boxes of the chlorine contact basins RAS and WAS Pumping To maintain an inventory of biomass (microorganisms), solids settled in the secondary clarifiers are continually returned to the aeration basins. The RAS flow from the four square clarifiers is pumped from the RAS wet well by any combination of six RAS pumps, each with a maximum capacity of 2,360 gallons per minute (gpm). The RAS flow from the circular October 2014 FINAL DRAFT 7-9 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

29 clarifier is pumped by one of two dedicated RAS pumps, each with a maximum capacity of 4,420 gpm. All of the RAS pumps are equipped with variable frequency drives (VFDs), so that RAS flow can be paced with WWTP influent flow. Historically, RAS has been pumped at an average rate equivalent to approximately 100 percent of the plant influent flow. However, the WWTP is currently operating the RAS pumps at a flow rate equivalent to 70 percent of the influent flow rate. The WAS pump station pumps excess solids generated in the secondary treatment process to the sludge thickening facilities. WAS is pumped from the 24-inch RAS line and piped to the DAFT for thickening prior to digestion. The WWTP currently wastes 24 hours per day, 7 days per week Effluent Pressure Filters There are six pressurized effluent filters at the WWTP, but one is currently out of service and requires extensive repair prior to being brought back on-line. Filtration of the secondary effluent is used to meet permit requirements for TSS, especially the more stringent summer requirements. A portion of the secondary effluent is typically pumped to the effluent filters through motorized valves on the discharge header of the Filter Feed Pump Station. Flow passes down through the mixed media, where solids are trapped. The media is supported by layers of gravel over the underdrain system. Filtered effluent is discharged through motorized control valves and is piped into the filtration bypass line that flows to the chlorine contact basin influent mixing boxes. Accumulated solids are flushed out of the filters by periodically pumping filtered effluent up through the media from the bottom. This backwashing can either be initiated manually or automatically based on time or high headloss through the filters Disinfection Facilities Prior to final discharge, partially filtered secondary effluent is disinfected with sodium hypochlorite. When there are peak flows greater than 40 mgd, primary effluent can be blended with the secondary effluent at the head of Chlorine Contact Basin 2 prior to hypochlorite injection. Disinfection facilities include two chlorine contact basins, chemical metering pumps and chemical storage tanks. Partially filtered secondary effluent flows through the influent channel, where it is distributed between two chlorine contact basins to the influent mixing boxes. Chemical feed pumps, located on the deck next to the contact basins, meter sodium hypochlorite from the two 1,000-gallon day tanks into each contact basin. At the entrance to the contact basins, chemical induction units diffuse and mix the sodium hypochlorite with the contact basin influent flow. Four 10,500-gallon bulk storage tanks are located at the sodium hypochlorite facility on the northeast side of the WWTP. Transfer pumps pump sodium hypochlorite solution from the bulk storage tanks to the day tanks. October 2014 FINAL DRAFT 7-10 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx

30 Each contact basin has a serpentine arrangement with five passes to maximize contact with the sodium hypochlorite and minimize short-circuiting. Each basin has a length of 122 feet and a width of 37 feet, for a total volume of approximately 710,000 gallons. Prior to discharge, the disinfected effluent is dechlorinated with sodium bisulfite. The bisulfite solution is fed on the downstream side of each contact basin. Bisulfite feed pumps and bulk storage tanks are located in the Bisulfite Storage Facility. Each contact basin has an effluent weir that sets the level in the basin. Disinfected effluent flows over the effluent weirs and travels by gravity to the effluent pump station wet well for final discharge through the outfall and to the Bay Effluent Pumping Final effluent is pumped through the outfall by either of the two effluent pump stations, which discharge into a common header. A surge tank protects the outfall line from surges. Sampler pumps, automatic samplers, and a bioassay system are also located in the pump station Effluent Pump Station No. 1 Effluent Pump Station No. 1, which is used for normal dry-weather flow conditions, has four pumps, each equipped with a VFD. Two of the pumps have a rated capacity of 5,000 gpm each and two have a rated capacity of 9,000 gpm each. The pump controls are based on maintaining a level setpoint in the wet well Effluent Pump Station No. 2 Effluent Pump Station No. 2, which is used only for extreme wet-weather events, has three constant speed pumps, each with a rated capacity of 13,880 gpm. The pumps have soft starts and can be controlled by modulating the discharge valves to maintain a level setpoint, but they are typically operated manually Effluent Outfall Treated wastewater is discharged at Discharge Point 001 to the lower San Francisco Bay via a submerged outfall equipped with a multi-port diffuser. The outfall is approximately 3,700 feet offshore and 500 feet north of the San Mateo Bridge at a depth of approximately 40 feet below the mean WSE. In September 2012, Underwater Resources, Inc. (URI), performed an exterior condition assessment of the outfall diffuser and in October 2012, URI performed an interior condition assessment of approximately 3,100 feet of the outfall. Results from the condition assessments are included in Appendix O. In Fall of 2014, the City completed the outfall repair project that was recommended in URI s condition assessment. Pictures and drawings from the repair project are also included in Appendix O. October 2014 FINAL DRAFT 7-11 pw://carollo/documents/client/ca/san Mateo/8562C01/Deliverables/Master Plan Report/SM_07.docx